This invention relates to steerable catheter-guidewire systems, more particularly to turn-limiters for steerable guidewire-directed catheter system, including "fixed-wire" angioplasty dilation balloon catheter-guidewire systems.
Steerable guidewire-directed catheter systems are systems that contain movable guidewire components. Directional control of these systems is accomplished by rotating, advancing, and/or retracting the guidewire components relative to the catheter components of these systems. Typically, the facility with which a steerable guidewire-directed catheter system can be advanced within the confines of a tortuous lumen varies as a function of the mobility of the guidewire component relative to the catheter component of the particular system. "Fixed-wire" angioplasty dilatation balloon catheter systems are steerable guidewire-directed catheter systems that are used to accomplish percutaneous transluminal balloon-mediated dilatation of intravascular lesions. Typically, "fixed-wire" angioplasty balloon catheter systems permit the performance of an angioplasty within the confines of lesions that frequently cannot accommodate "over-the-wire" systems. For example, U.S. Pat. No. 4,582,181 describes a "fixed-wire" angioplasty dilatation balloon catheter-guidewire system. These systems comprise, in general, a catheter component (composed, at least, of a proximal adapter, catheter shaft, and dilatation balloon) and a guidewire component (composed, at least, of a mandrel and a tip coil). "Fixed-wire" angioplasty catheter-guidewire systems are distinguished from other angioplasty systems by virtue of the mobility of the guidewire component relative to the catheter component of these systems. Specifically, "fixed-wire" systems afford variable rotational catheter-guidewire intercomponent mobility. However, these devices do not provide any corresponding coaxial catheter-guidewire inter-component mobility. Other things being equal, the directional control or "steerability" of a "fixed-wire" system varies directly with the rotational mobility of the guidewire component relative to the catheter component.
The construction of a hydraulically competent, single-channel "fixed-wire" angioplasty system requires the creation of a liquid-tight seal between the catheter and guidewire component at the distal catheter/guidewire interface. With many single-channel "fixed-wire" catheter systems of the prior art, adhesives have been typically used to create this interface. This approach effectively joins the balloon and guidewire components within the distal catheter/guidewire interface. As examples, U.S. Pat. Nos. 4,573,470, 4,582,181, 4,664,113, 4,715,378, 4,723,936, 4,793,350, 4,955,384 and Re 33,166 describe "fixed-wire" systems containing adhesive seals.
The practice of joining the catheter component to the guidewire component, in the construction of these systems, subjects the balloon and guidewire components to shear forces during uni-directional rotation of the guidewire components relative to the catheter components. Excessive uni-directional rotation of the guidewire components relative to the catheter components predisposes these systems to the development of balloon wrapping, balloon rupture and guidewire fracture. In general, these systems tolerate less than 5-8 uni-directional guidewire revolutions for this reason.
Turn limiters have been developed to limit the number of uni-directional turns that can be applied to the guidewire components of "fixed-wire" angioplasty catheter-guidewire systems, and to prevent the development of structural damage to these systems due to excessive uni-directional guidewire rotation. For example, U.S. Pat. No. 4,664,113 describes a rotation or turn limiter, the functional mechanism of which is comprised of a stack of inter-locking discs. Each disc contains a groove and an arresting pin. The groove of one disc is designed to receive the arresting pin of the adjacent disc. U.S. Pat. No. 4,619,263 describes a turn limiter device which uses a rotational torque knob to drive the guidewire, the torque knob threading into and out of a thumb screw. The torque knob includes arms which functionally limit the longitudinal distance the torque knob can travel, thereby limiting the rotation of the guidewire. This structure causes the guidewire to move longitudinally as it rotates, due to the translation of the torque knob.
The above turn-limiters were developed specifically for use in conjunction with "fixed-wire" devices that accommodate less than 4-5 uni-directional revolutions of the guidewire components relative to the catheter components. These prior art turn limiters complicate the angioplasty procedure because they commonly require the operator to periodically stop the procedure and unwind the guidewire to its "home" position as the operator negotiates the catheter system through the convoluted arteries of the patient's cardiovascular system. Clearly, the frequency with which the operator is required to unwind a "fixed-wire" system varies inversely with the rotational capacity of the particular system, which, in turn, relates to the rotational capacity of either: (1) the catheter-guidewire interface or (2) the turn-limiter. Systems of the prior art that accommodate less than 4-5 uni-directional guidewire turns commonly provoke significant distraction to the operator. Typically, these systems provide no information to the operator regarding the rotational status of the guidewire component relative to the catheter component and hence these systems are prone to require unwinding without notice.
An advanced "fixed-wire" system capable of accommodating a considerably greater number of uni-direction guidewire rotations has been developed by Danforth BioMedical, Inc. of Menlo Park, Calif. ("DBI"), and is subject to U.S. patent application Ser. No. 615,721, filed on Nov. 19, 1990. This device affords superior directional control and provokes less interruption to the performance of the procedure relative to the prior art. The device, however, requires a turn limiter that accommodates upwards of twenty uni-directional guidewire revolutions.
No prior art turn limiter is particularly suitable for use in conjunction with such an advanced fixed-wire system. The maximum number of uni-directional turns that can be accommodated by the device described in U.S. Pat. No. 4,664,113, for example, varies as a function of the number of discs that are stacked together in the construction of the mechanism. Each disc contributes less than one full revolution. Modifying this turn limiter to accommodate twenty uni-directional guidewire rotations would require stacking more than twenty interlocking discs together in the construction of the functional mechanism. Although feasible, this approach is disadvantageous in that it results in the generation of a particularly complex, multi-component, elongated device that would be expensive to manufacture and cumbersome to handle.
The operation of the turn limiter described in U.S. Pat. No. 4,619,263 causes the guidewire component to advance or retract relative to the catheter component as it is rotated. The magnitude of coaxial catheter-guidewire translation that develops in response to rotation of the guidewire component varies as a function of the number of uni-direction turns that are applied to the system. The use of this turn-limiter in conjunction with the DBI "fixed-wire" device previously described would result in significant coaxial expansion or contraction of the composite system. Therefore, the use of this turn-limiter in conjunction with a device such as the DBI device would further disrupt the spatial relationship between the proximal end of the guidewire tip coil and the distal end of the balloon component of the DBI system and thereby disrupt the surface contour of the distal catheter/guidewire transition. This circumstance, in turn, could adversely influence the surface resistance of the distal aspect of the composite system.
From the foregoing it becomes evident that the directional control of a "fixed-wire" catheter/guidewire system varies directly as a function of the rotational mobility of the guidewire component relative to the catheter component of the system. Therefore, it is foreseeable that future "fixed-wire" devices will continue to be developed to provide superior guidewire rotational mobility relative to conventional devices. Turn-limiting devices must be employed to prevent excessive uni-directional rotation of the guidewire components disposed within the catheter components of selected "fixed-wire" systems. Prior art turn limiters, however, are particularly suited for use in conjunction with devices that only tolerate less than 4-6 uni-directional guidewire rotations.
The advent of "fixed-wire" devices that afford uni-directional enhanced guidewire rotational mobility relative to the prior art create the need for turn-limiters that permit substantially greater uni-directional guidewire rotational mobility, that are easy to construct, and that do not provoke coaxial translation of the guidewire component relative to the catheter component consequent with intercomponent rotation. Hereinafter is described a turn limiter that meets these and other needs.